[35] RT-PCR Analysis for FGF23 Using Paraffin Sections in the Diagnosis of Phosphaturic Mesenchymal Tumors with and without Known Tumor Induced Osteomalacia: A Study of 27 Cases

A Bahrami, RV Lloyd, SW Weiss, E Montgomery, AE Horvai, L Jin, CY Inwards, AL Folpe. Mayo Clinic, Rochester, MN; Emory University, Atlanta, GA; Johns Hopkins Medical Institutions, Baltimore, MD; UCSF, San Francisco, CA

Background: Phosphaturic mesenchymal tumors of the mixed connective tissue type (PMTMCT) are extremely rare, histologically distinctive neoplasms which cause tumor-induced osteomalacia (TIO) in most cases through elaboration of a phosphaturic hormone, fibroblast growth factor-23 (FGF-23). Rarely, identical tumors without known TIO may be seen. We studied a large group of PMTMCT for expression of FGF-23, utilizing a novel RT-PCR assay for FGF-23 in formalin-fixed, paraffin-embedded (FFPE) tissues.
Design: 27 PMTMCT (14 with, 13 w/o TIO) and 11 non-PMTMCT (6 chondromyxoid fibromas (CMF), 2 chondroblastomas, 1 SFT, 1 osteosarcoma, 1 paraganglioma) were retrieved. Total RNA was extracted from FFPE sections for RT-PCR analysis. FGF23 was amplified using three sets of primers that spanned the intron/exon boundaries to amplify the three exons of FGF23 gene (140 bp, 125bp, and 175 bp). The housekeeping gene phosphoglycerokinase (PGK, 189bp) was co-amplified to check RNA quality. Products were visualized by Agilent 2100 Bioanalyzer, Agilent DNA 1000 Kit and DNA chips. 2 PMTMCT with TIO, 3 PMTMCT without TIO and 5 non-PMTMCT lacked a positive PGK control and were excluded.
Results: 11 of 12 (92%) PMTMCT with known TIO were FGF23-positive. 9 of 13 (69%) PMTMCT without known TIO were FGF23-positive. One CMF was positive; all other non-PMTMCT were negative.
Conclusions: We conclude that RT-PCR for FGF-23 is a sensitive and specific means of confirming the diagnosis of PMTMCT both in patients with and without TIO. FGF-23 gene expression was present in >90% of PMTMCT with known TIO, confirming the role of FGF-23 in this syndrome. Rare FGF-23-negative PMTMCT with known TIO likely express other phosphaturic hormones (e.g., frizzled related protein 4). Our finding of expression of FGF-23 in 69% of histologically identical tumors without known TIO confirms the reproducibility of the diagnosis of PMTMCT, even in the absence of known phosphaturia. FGF-23-positive PMTMCT without known TIO were likely excised prior to becoming symptomatic. The exact nature of FGF-23-negative putative PMTMCT without TIO is unclear, although histological re-review did not suggest alternative diagnoses. Ongoing study of additional non-PMTMCT should further establish the frequency of FGF-23 expression in other tumor types.
Category: Bone & Soft Tissue

Tuesday, March 10, 2009 9:30 AM

Poster Session III # 8, Tuesday Morning